1. Filed of the Invention
The present invention relates to an apparatus for detecting an abnormality of a pressure regulator for regulating, to an appropriate pressure, the pressure of liquified propane gas accommodated in a gas bottle or a gas supplied in bulk and supplied to a gas instrument under a high pressure or for detecting a gas leakage which has occurred in a gas supply pipe and a method to be carried out by the apparatus.
2. Description of the Related Arts
A gas meter incorporating a gas cutoff device has been developed in recent years in order to prevent an explosion due to gas leakage or a fire which occurs due to a failure in turning off the gas. The gas cutoff device has a function of stopping a gas supply when a signal indicating the occurrence of gas leakage has been detected. If it is decided by the gas cutoff device that the gas has been in use for a long time and thus the gas has not been turned off, the gas cutoff device stops the supply of gas. Owing to this cutoff operation, gas leakage or an abnormal pressure can be prevented from occurring in the range downstream of the gas meter, namely, on the gas instrument side of a gas supply equipment.
Inspections for safety control of the side upstream of the gas meter, namely, the range between a gas bottle and the gas meter is performed by an employee of a propane gas supplier who goes to the gas supply equipment once every two years.
FIG. 1 is a block diagram showing the construction of a conventional gas supply equipment to be checked for safety. The gas supply equipment comprises a gas bottle 1 containing liquefied propane gas 1, a cock 2, a pressure regulator 3, a gas meter 4, a gas burning instrument or combustor 5, a pressure gauge 6, and a pen recorder 7 for recording the change in gas pressure.
The safety check operation of the gas supply equipment of this construction is performed as follows. An operator visits the gas supply equipment once every two years where the operator interposes the pressure gauge 6 and the pen recorder 7 between the pressure regulator 3 and the gas meter 4 so that the pen recorder 7 records a gas pressure inside the gas pipe. In order to check for the leakage of gas between the pressure regulator 3 and the gas meter 4, the operator closes a cutoff valve incorporated in the gas meter 4 and the cock 2 of the gas bottle 1. If gas leakage has occurred, the pen recorder 7 records a gas pressure which has dropped with the passage of time. In this manner, an abnormal state of the gas pipe can be checked. The pressure adjusting capability of the pressure regulator 3 is checked by the following method. The operator opens the cock 2 and a cutoff valve disposed inside the gas meter 4 to cause the gas burning instrument 5 to be used in a normal condition so that a gas pressure is measured by the pressure gauge 6. If a gas pressure ranges from 2300 to 3300 Pascal (Pa), it is decided that the pressure regulator 3 has a normal pressure adjusting capability, whereas if a gas pressure is not in this range, it is decided that the pressure regulator 3 has an abnormal pressure adjusting capability.
It takes time and labor for the operator to visit the gas supply equipment so as to perform safety check by installing measuring devices on the gas supply equipment. In addition, the operator goes to the gas supply equipment at an interval of two years, which is long in ensuring the safety of the gas supply equipment.
In order to solve this problem, abnormality detecting apparatuses have been developed and disclosed in Japanese Laid-Open Patent Publications No. 4-76312 and 2-201509. The apparatuses were developed to monitor gas leakage which may occur in a gas supply pipe or abnormality of a gas pressure regulator constantly or frequently.
The apparatus according to Japanese Laid-Open Patent Publication No. 4-76312 comprises a pressure detecting means for detecting a gas pressure in a gas supply pipe downstream of a pressure regulator serving as a gas supply equipment; a timer means controlled by a signal outputted from the pressure detecting means; a deciding means for deciding whether or not the gas supply equipment has an abnormality on receipt of a signal outputted from the timer means; and an alarm giving means for outputting an alarm signal on receipt of a signal outputted from the deciding means.
FIG. 2 is a block diagram showing the abnormality detecting apparatus according to Japanese Laid-Open Patent Publications No. 4-76312. The apparatus comprises a gas bottle containing liquefied propane gas 1, a cock 2, a pressure regulator 3, and a gas meter 4 accommodating a pressure sensor 8 serving as a pressure detector; a timer means 9; a deciding unit 10; an alarm generator 11; and a gas burning instrument or combustor 5.
When the pressure regulating function of the pressure regulator 3 operates normally, a gas pressure in the gas supply equipment is kept in the range from 2300 to 3300 Pa when gas is used by the gas burning instrument 5. But when the gas burning instrument 5 is not used, the temperature of LP gas enclosed inside the gas pipe rises even though the pressure regulator 3 is normal. This is because the gas supply equipment is subjected to sunshine. As a result, the pressure of gas pressure rises due to the expansion thereof. Consequently, the gas pressure may exceed 3300 Pa. Therefore, it is necessary to decide whether the pressure rise has occurred due to the abnormality of the pressure regulator 3 or due to temperature rise in outside temperature. In the apparatus having the above-described construction, a decision as to the pressure regulator 3 is normal or not is made by utilizing the characteristic of pressure that a pressure change is comparatively slow in the case of pressure rise due to temperature rise and a pressure which has risen to a certain value in several minutes is kept for more than 24 hours. That is, when a signal indicating that the cutoff pressure of the pressure regulator 3 exceeds 3300 Pa and the cutoff pressure is greater than 3300 Pa for as long as 24 hours as a result of turn-off of the gas burning instrument 5, it is decided that the gas pressure inside the pressure regulator 3 is abnormal. When the gas pressure of the pressure regulator 3 is less than 3300 Pa as a result of turn-off of the gas burning instrument 5, the timer means 9 starts counting time and the deciding unit 10 monitors signals outputted from the timer means 9 and the pressure sensor 8. If a pressure indicated by signals outputted from the pressure sensor 8 is less than 3300 Pa for 30 days continuously, the deciding unit 10 decides that gas leakage has occurred, thus outputting a signal to the alarm generator 11. That is, the abnormality detecting apparatus detects an abnormality by utilizing the actual condition in that in 30 days, there is a day in which the gas instrument is not turned on and the gas pressure inside the gas pipe may rise due to a sunshine-caused temperature rise.
In the pressure regulating/measuring apparatus according to Japanese Patent Laid-Open Publication No. 2-201509, the pressure regulator and gas meter are constructed together as a unit. The apparatus comprises a means for generating a flow rate signal, a lower limit pressure detecting means, and an upper limit pressure detecting means. Turn-on and turn-off of the gas are detected by the means for generating a flow rate signal; a supply gas pressure is checked by signals outputted from the lower limit pressure detecting means and the upper limit pressure detecting means; a cutoff pressure is checked by the upper limit pressure detecting means; and gas leakage is detected by the means for generating a flow rate signal.
That is, the lower limit pressure detecting means and the upper limit pressure detecting means are constituted by a lead switch operated by a magnet installed on a diaphragm which is mounted in a pressure regulating portion and moved at a predetermined pressure or by a pressure switch of the semiconductor type. In this construction, when gas is being supplied, the pressure fluctuation cycle is 4-15 times per minute. If the pressure fluctuation cycle exceeds an upper limit of 4200 Pa 4-15 times per minute, it is decided that abnormality has not occurred in the pressure regulator. If the pressure fluctuation cycle does not exceed the upper limit 4200 Pa, it is decided that an abnormality has occurred in the pressure regulator.
In the above-described two conventional apparatuses, if the cutoff pressure adjusting capability of the pressure regulator is abnormal, only the abnormality of the cutoff pressure can be detected, whereas the apparatuses are not provided with techniques for checking the gas leakage of the gas pipe. Accordingly, even if it is decided that the cutoff pressure is abnormal, there are cases where the pressure regulator is not repaired or replaced promptly on the assumption that the abnormality of the cutoff pressure will not lead to an explosion or a fire soon. But in this case, there is a possibility that an explosion will occur.
In addition, the pressure adjusting capability of the pressure regulator which converts gas having a high pressure supplied from a gas bottle into gas having an appropriate combustible pressure range decreases gradually with the passage of time. It is preferable that the pressure adjusting capability of the pressure regulator can be kept to be constant. But in fact, the pressure adjusting capability of the pressure regulator decreases when the pressure regulator has a great flow rate of gas and in addition, the older the pressure regulator becomes, the lower the pressure adjusting capability becomes. Therefore, it is necessary to decide whether or not gas pressure is adjusted to a predetermined range in the state in which gas flow rate is more than a certain value.